System and method for operating a gas turbine

ABSTRACT

A system for operating a gas turbine includes a controller configured to execute logic stored in a memory that causes the controller to determine two or more of a frequency, a coherence, a phase, and an amplitude, of a combustion instability; to compare two of more of the frequency, the coherence, the phase, and the amplitude of the combustion instability to a respective predetermined limit; and to adjust at least one parameter of the gas turbine if two or more of the frequency, the coherence, the phase, and the amplitude of the combustion instability are actionable relative to their respective predetermined limits. A related method of operating the gas turbine is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/170,702, filed Feb. 3, 2014, which was granted Jan. 31, 2017, as U.S.Pat. No. 9,556,799, the entire disclosure of which is incorporated byreference herein.

TECHNICAL FIELD

The present invention generally involves a system and method foroperating a gas turbine. In particular embodiments, the system andmethod may be incorporated into the gas turbine or other turbomachine todetect the possibility of and/or reduce unwanted vibrations in hot gaspath components downstream from a combustion system, resulting fromin-phase, coherent combustion tones.

BACKGROUND

Combustors are commonly used in industrial and commercial operations toignite fuel to produce combustion gases having a high temperature andpressure. For example, gas turbines and other turbomachines typicallyinclude one or more combustors to generate power or thrust. A typicalgas turbine used to generate electrical power includes an axialcompressor at the front, multiple combustors around the middle, and aturbine at the rear. Ambient air enters the compressor as a workingfluid, and the compressor progressively imparts kinetic energy to theworking fluid to produce a compressed working fluid at a highlyenergized state. The compressed working fluid exits the compressor andflows through one or more fuel injectors in the combustors where thecompressed working fluid mixes with fuel before igniting to generatecombustion gases having a high temperature and pressure. The combustiongases flow to the turbine where they expand to produce work. Forexample, expansion of the combustion gases in the turbine may rotate ashaft connected to a generator to produce electricity.

At particular operating conditions, combustion dynamics at specificfrequencies and with sufficient amplitudes, which are in phase andcoherent, may produce undesirable sympathetic vibrations in the turbineand/or other downstream components. In the context of this invention,coherence refers to the strength of the linear relationship between two(or more) dynamic signals, which is strongly influenced by the degree offrequency overlap between them. Typically, this problem is managed bycombustor tuning which limits the amplitude of the combustion dynamicsin a particular frequency band. However, combustor tuning mayunnecessarily limit the operating range of the combustor.

Altering the frequency, coherence, phase, and/or amplitude of thecombustors may reduce unwanted vibrations of the turbine and/or otherdownstream components. One approach to reducing unwantedcombustion-driven vibrations in downstream components is to alter thecoherence of the combustion system. For instance, as the frequency ofthe combustion dynamics in one or more, but not all, combustors isdriven away from that of the other combustors, coherence and, therefore,modal coupling of the combustion dynamics of the combustors is reduced,which, in turn, reduces the ability of the combustor tone to cause avibratory response in downstream components. Alternatively, shifting thecombustion dynamics frequency of each of the combustors away from thenatural frequency of the downstream components may also reduce unwantedvibrations of downstream components.

Therefore, a system and method for operating a gas turbine that detectsthe possibility of unwanted vibrations in downstream components and/orreduces such unwanted vibrations by altering the frequency, phase,amplitude, and/or coherence between combustors would be useful forenhancing the thermodynamic efficiency of the combustors, protectingagainst accelerated wear, promoting flame stability, and/or reducingundesirable emissions over a wide range of operating levels, withoutdetrimentally impacting the life of the downstream hot gas pathcomponents.

SUMMARY

Aspects and advantages of the invention are set forth below in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One embodiment of the present invention is a system for operating a gasturbine, which includes: a compressor section configured to receiving aworking fluid and to produce a compressed working fluid; and a pluralityof combustors downstream from the compressor section, wherein eachcombustor includes a fuel injector that receives fuel at a fueltemperature and a fuel flow rate. A controller is configured to executelogic stored in a memory that causes the controller: to determine atleast a frequency of a combustion instability and a coherence of acombustion instability; to compare the frequency of the combustioninstability to a predetermined frequency limit and the coherence of thecombustion instability to a predetermined coherence limit; and to adjustat least one parameter of the gas turbine if the frequency of thecombustion instability is actionable relative to the predeterminedfrequency limit and the coherence of the combustion instability isactionable relative to the predetermined coherence limit.

A method for operating a gas turbine includes: determining a frequencyof a combustion instability, and comparing the frequency of thecombustion instability to a predetermined frequency limit. The methodfurther includes: determining a coherence of a combustion instability,and comparing the coherence of the combustion instability to apredetermined coherence limit. If the frequency of the combustioninstability is actionable relative to the predetermined frequency limit,and the coherence of the combustion instability is actionable relativeto the predetermined coherence limit, the method adjusts at least oneparameter of the gas turbine.

According to other embodiments, the system or method may further includecomparing one of the frequency and the coherence of the combustioninstability to a predetermined time limit. In this or other embodiments,the system or method may further be employed to determine the amplitudeand/or the phase of the combustion instability; to compare the amplitudeto a predetermined amplitude limit and/or to compare the phase to apredetermined phase limit, and to adjust at least one parameter of thegas turbine is at least one of the amplitude and the phase of thecombustion instability is actionable relative to a predetermined limit.

The parameters being adjusted by the system or through the practice ofthe method may include one or more of: a temperature of the compressedworking fluid; a flow rate of the working fluid; a flow rate of thecompressed working fluid recirculated through the compressor section;the fuel flow rate of the fuel to at least one injector; and the fueltemperature of the fuel to at least one injector.

Those of ordinary skill in the art will better appreciate the featuresand aspects of such embodiments, and others, upon review of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a simplified side cross-sectional view of an exemplary gasturbine according to various embodiments of the present disclosure;

FIG. 2 is a simplified side cross-sectional view of an exemplarycombustor according to various embodiments of the present disclosure;

FIG. 3 is an upstream plan view of the cap assembly shown in FIG. 2according to an embodiment of the present disclosure;

FIG. 4 is an upstream plan view of the cap assembly shown in FIG. 2according to an alternate embodiment of the present disclosure;

FIG. 5 is a simplified side cross-section view of a system according tovarious embodiments of the present disclosure;

FIG. 6 is a diagram of a system according to alternate embodiments ofthe present disclosure; and

FIG. 7 is an exemplary flow diagram of a method for operating a gasturbine according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

As used herein, the terms “first,” “second,” and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify either the location or the importance of theindividual components.

The terms “upstream,” “downstream,” “radially,” and “axially” refer tothe relative direction with respect to fluid flow in a fluid pathway.For example, “upstream” refers to the direction from which the fluidflows, and “downstream” refers to the direction to which the fluidflows. Similarly, “radially” refers to the relative directionsubstantially perpendicular to the fluid flow, and “axially” refers tothe relative direction substantially parallel to the fluid flow.

Each example is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that modifications and variations can be made in thepresent invention without departing from the scope or spirit thereof.For instance, features illustrated or described as part of oneembodiment may be used on another embodiment to yield a still furtherembodiment. Thus, it is intended that the present invention covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents.

Various embodiments of the present invention include a system and methodfor operating a gas turbine to detect the possibility of unwantedvibrations in hot gas path components downstream from the combustionsystem and/or reduce such unwanted vibrations, which may result fromin-phase, coherent combustion tones. The system and method may beimplemented in a gas turbine having multiple combustors, and eachcombustor may include one or more fuel injectors for mixing fuel with acompressed working fluid prior to combustion. The system and method mayfurther include a controller configured to execute logic stored in amemory that causes the controller to determine a frequency, a coherence,and, optionally, a phase and/or an amplitude, of one or more combustioninstabilities; to compare the frequency, the coherence, and, optionally,the phase and/or the amplitude, of the one or more combustioninstabilities to a predetermined limit; and adjust at least oneparameter of the gas turbine if the frequency, the coherence, and,optionally, the phase and/or the amplitude, of the one or morecombustion instabilities is actionable relative to the predeterminedlimit.

As used herein, the phrase “actionable relative to the predeterminedlimit” is dependent on the particular parameter being compared.Specifically, this phrase means that the parameter is either within adesignated range (e.g., for frequency), less than a lower predeterminedlimit (e.g., for phase), or greater than an upper predetermined limit(e.g., for coherence or amplitude). It is to be understood that, invarious embodiments, two, three, or four characteristics may bedetermined to be actionable relative to their predetermined limitsbefore the system (or method) performs an action.

The system and method may adjust at least one parameter in response tothe detection of a condition that is actionable relative to thepredetermined limit. For example, the system and method may adjust atemperature, pressure, and/or flow rate of a compressed working fluidproduced by a compressor section of the gas turbine. Alternately, or inaddition, the system and method may adjust a fuel flow and/or fueltemperature to one or more fuel circuits in one or more of thecombustors. As a result, various embodiments of the present disclosuremay reduce the ability of the combustor tone to cause a vibratoryresponse in downstream components.

Although exemplary embodiments of the present invention will bedescribed generally in the context of the combustion dynamics in a gasturbine for purposes of illustration, one of ordinary skill in the artwill readily appreciate that embodiments of the present disclosure maybe applied to any combustion dynamics and are not limited to a gasturbine unless specifically recited in the claims.

Referring now to the drawings, FIG. 1 provides a simplified sidecross-sectional view of an exemplary gas turbine 10 that may incorporatevarious embodiments of the present disclosure. As shown, the gas turbine10 may generally include an inlet section 12, a compressor section 14, acombustion section 16, a turbine section 18, and an exhaust section 20.The inlet section 12 may include a series of filters 22 and one or morefluid conditioning devices 24 to clean, heat, cool, moisturize,de-moisturize, and/or otherwise condition a working fluid 28 (e.g., air)entering the gas turbine 10. The cleaned and conditioned working fluid28 flows to a compressor 30 in the compressor section 14. A compressorcasing 32 contains the working fluid 28, as alternating stages ofrotating blades 34 and stationary vanes 36 progressively accelerate andredirect the working fluid 28 to produce a continuous flow of compressedworking fluid 38 at a higher temperature and pressure.

The majority of the compressed working fluid 38 flows through acompressor discharge plenum 40 to one or more combustors 42 in thecombustion section 16. A fuel supply 44 in fluid communication with eachcombustor 42 supplies a fuel to each combustor 42. Possible fuels mayinclude, for example, blast furnace gas, coke oven gas, natural gas,methane, vaporized liquefied natural gas (LNG), hydrogen, syngas,butane, propane, olefins, diesel, petroleum distillates, andcombinations thereof. The compressed working fluid 38 mixes with thefuel and ignites to generate combustion gases 46 having a hightemperature and pressure.

The combustion gases 46 flow along a hot gas path through a turbine 48in the turbine section 18 where they expand to produce work.Specifically, the combustion gases 46 may flow across alternating stagesof stationary nozzles 50 and rotating buckets 52 in the turbine 48. Thestationary nozzles 50 redirect the combustion gases 46 onto the nextstage of rotating buckets 52, and the combustion gases 46 expand as theypass over the rotating buckets 52, causing the rotating buckets 52 torotate. The rotating buckets 52 may connect to a shaft 54 that iscoupled to the compressor 30 so that rotation of the shaft 54 drives thecompressor 30 to produce the compressed working fluid 38. Alternately orin addition, the shaft 54 may connect to a generator 56 for producingelectricity. Exhaust gases 58 from the turbine section 18 flow throughthe exhaust section 20 prior to release to the environment.

FIG. 2 provides a simplified side cross-section view of an exemplarycombustor 42 according to various embodiments of the present invention.As shown in FIG. 2, a combustor casing 60 and an end cover 62 maycombine to contain the compressed working fluid 38 flowing to thecombustor 42. A cap assembly 64 may extend radially across at least aportion of the combustor 42, and one or more fuel injectors 66, 68 maybe radially arranged across the cap assembly 64 to supply fuel to acombustion chamber 70 downstream from the cap assembly 64. A liner 72may circumferentially surround at least a portion of the combustionchamber 70, and a transition duct 74 downstream from the liner 72 mayconnect the combustion chamber 70 to the inlet of the turbine 48. Animpingement sleeve 76 with flow holes 78 may circumferentially surroundthe transition duct 74, and a flow sleeve 88 may circumferentiallysurround the liner 72. With these features, the compressed working fluid38 may pass through the flow holes 78 in the impingement sleeve 76 toflow through an annular passage 80 outside of the transition duct 74 andliner 72. When the compressed working fluid 38 reaches the end cover 62,the compressed working fluid 38 reverses direction to flow through thefuel injectors 66 and into the combustion chamber 70. The combustors 42may be any type of combustor known in the art, and the presentdisclosure is not limited to any particular combustor design unlessspecifically recited in the claims.

FIGS. 3 and 4 provide upstream plan views of exemplary arrangements ofthe fuel injectors 66, 68 in the cap assembly 64 within the scope of thepresent disclosure. As shown in FIG. 3, for example, multiple fuelinjectors 66 may be radially arranged around a single fuel injector 66.Alternatively, a plurality of non-circular, truncated pie-shaped fuelinjectors 68 may circumferentially surround a single circular fuelinjector 66, as shown in FIG. 4.

Although generally shown as cylindrical (in FIGS. 2 and 3), the radialcross-section of the fuel injectors 66, 68 may be any geometric shape,and the present disclosure is not limited to any particular radialcross-section unless specifically recited in the claims. One of ordinaryskill in the art will readily appreciate multiple other shapes andarrangements for the fuel injectors 66, 68 from the teachings herein,and the particular shape and arrangement of the fuel injectors 66, 68are not limitations of the present invention unless specifically recitedin the claims. In addition, various embodiments of the combustor 42 mayinclude different numbers and arrangements of fuel injectors 66, 68 inthe cap assembly 64.

The fuel injectors 66, 68 may be divided into various groups or circuitsto facilitate multiple fueling regimes over a wide range of operations.In the exemplary arrangements shown in FIGS. 3 and 4, the center fuelinjector 66 and/or one of the outer fuel injectors 66, 68 may receivefuel from a first fuel circuit 82, while one or more of the surroundingfuel injectors 66, 68 may be grouped to receive the same or a differentfuel from a second and/or third fuel circuit 84, 86. During base loadoperations, fuel may be supplied to each fuel injector 66, 68 via one ofthe three fuel circuits 82, 84, 86, while fuel flow may be reduced orcompletely eliminated from one or more of the fuel injectors 66, 68during reduced or turndown operations. Altering the fuel split to eachfuel circuit 82, 84, 86 in one or more combustors 42 may alter thefrequency, phase, amplitude, and/or coherence of the combustiondynamics.

An overlap between the frequency of the combustion dynamics and thedownstream component resonant frequency may result in unwanted vibrationof the downstream components when an in-phase and coherent relationshipbetween the combustion dynamics frequencies of two or more combustors 42exists. Various embodiments of the present disclosure seek to detect thepossibility of unwanted vibrations in hot gas path components downstreamfrom the combustion system and/or to reduce such unwanted vibrations bydetermining a frequency, a coherence, and, optionally, a phase and/or anamplitude, of one or more combustion instabilities; comparing thefrequency, the coherence, and, optionally, the phase and/or amplitude,of the one or more combustion instabilities to a predetermined limit;and adjusting at least one parameter of the gas turbine if thefrequency, the coherence, and, optionally, the phase and/or theamplitude, of the one or more combustion instabilities is actionablerelative to the predetermined limit. In this manner, the embodiments ofthe present disclosure may detect and/or reduce unwanted vibrations inhot gas path components downstream from the combustion system over awide range of operating levels.

FIG. 5 provides a simplified cross-sectional view of a system 90 foroperating the combustors 42, according to various embodiments of thepresent disclosure. As shown in FIG. 5, the system 90 may beincorporated into the gas turbine 10 (previously described with respectto FIG. 1) and may include a controller 92 configured to execute logic94 stored in a memory 96.

The controller 92 may generally be any suitable processing device knownin the art, and the memory 96 may generally be any suitablecomputer-readable medium or media, including, but not limited to, RAM,ROM, hard drives, flash drives, or other memory devices. As is generallyunderstood, the memory 96 may be configured to store informationaccessible by the controller 92, including instructions or logic 94 thatcan be executed by the controller 92. The instructions or logic 94 maybe any set of instructions that when executed by the controller 92 causethe controller 92 to provide the desired functionality.

For instance, the instructions or logic 94 may be software instructionsrendered in a computer-readable form. When software is used, anysuitable programming, scripting, or other type of language orcombinations of languages may be used to implement the teachingscontained herein. Alternatively, the instructions can be implemented byhard-wired logic or other circuitry, including, but not limited toapplication-specific circuits.

The technical effect of the controller 92 is to execute the logic 94stored in the memory 96 to cause the controller 92 to determine thefrequency, the coherence and, optionally, the phase and/or the amplitudeof one or more combustion instabilities. For example, the controller 92may receive a dynamic pressure signal 98 from each combustor 42, and thelogic 94 may enable the controller 92 to calculate the frequency and/oramplitude of each combustion instability for each combustor 42. Inaddition, the logic 94 may enable the controller 92 to calculate theaverage or median frequency, phase, amplitude, and/or coherence of someor all of the combustors 42.

The method by which average or median values are determined may vary fordifferent combustion instabilities and for different types of combustors42. For example, the average or median coherence may be determined asthe average or median of the coherence, or the square root of thecoherence, measured (a) for one or more combustion instability, (b)between one or more pairs of adjacent combustors 42, (c) between one ormore pairs of combustors 42, and/or (d) for one or more combustors 42with respect to a predetermined reference combustor 42. It has beenfound that the square root of coherence functions as an adequatesurrogate for the coherence itself and may simplify certaincomputational processes.

Similarly, the average or median phase may be determined as the averageor median of the absolute value of the phase measured (a) for one ormore of the combustion instabilities, (b) between one or more pairs ofadjacent combustors 42, (c) between one or more pairs of combustors 42,and/or (d) for one or more combustors 42 with respect to a predeterminedreference combustor 42.

It is important to note that a dynamic pressure signal is not requiredfor all combustors. Certainly, it is beneficial to have a dynamicpressure signal from each combustor. However, in the event that thedynamic pressure signal is identified as faulty or unavailable for oneor more combustors 42, the dynamic pressure signal may be excluded fromthe determination of average or median phase and/or coherence.

The logic 94 may further cause the controller 92 to compare thefrequency, the coherence, and, optionally, the phase and/or theamplitude, of the one or more combustion instabilities to apredetermined limit; and to adjust at least one parameter of the gasturbine 10 if the frequency, the coherence, and, optionally, the phaseand/or the amplitude, of the one or more combustion instabilities isactionable relative to the predetermined limit.

As used herein, the phrase “actionable relative to the predeterminedlimit” is dependent on the particular parameter being compared and meansthat the parameter is either within a designated range (e.g., forfrequency), less than a lower predetermined limit (e.g., for phase), orgreater than an upper predetermined limit (e.g., for coherence oramplitude). It is to be understood that, in various embodiments, two,three, or four characteristics may be determined to be actionablerelative to their predetermined limits before the system (or method)performs an action. The predetermined limits may vary for differentcombustion instability frequencies for each combustor 42 and may varyfor different combustor 42 and gas turbine 10 configurations. Therefore,it should be understood that the predetermined limits for frequency,phase, amplitude, and coherence may be set to any value.

In an exemplary embodiment, if the frequency is actionable relative tothe predetermined frequency limit by being within the designatedfrequency range, the phase is actionable relative to the predeterminedphase limit by being less than the predetermined phase limit, theamplitude is actionable relative to the predetermined amplitude limit bybeing greater than the predetermined amplitude limit, and/or thecoherence is actionable relative to the predetermined coherence limit bybeing greater than the predetermined coherence limit, then the system 90may take corrective action to reduce unwanted vibrations in hot gas pathcomponents downstream from the combustion system.

One particular method contemplated herein includes the determination ofeach of the frequency, amplitude, phase, and coherence, prior toadjusting any parameter of the gas turbine, since a determination ofthese four characteristics provides the most information with respect tothe behavior of the combustion dynamics of the combustors 42. However,for some configurations, such as those of a mature fleet withsignificant operating experience, it may be possible to adjust aparameter of the gas turbine based only on a determination of frequencyand coherence. In this instance, the additional operating experience mayprovide pre-existing knowledge of the phase, such that the phasecharacteristics can be assumed, as opposed to being determined as partof the present method.

The system 90 may include various means for adjusting at least oneparameter of the gas turbine 10 if the frequency, the coherence, and,optionally, the phase and/or the amplitude, of the one or morecombustion instabilities is actionable relative to the predeterminedlimits of frequency, coherence, and, optionally, phase and/or amplitude.For example, a change in the temperature, pressure, and/or flow rate ofthe compressed working fluid 38 produced by the compressor section 14directly affects the frequency and/or amplitude of each combustor 42. Inturn, a change in the frequency and/or amplitude may change the phaseand/or coherence of the combustion section 16. The system 90 may includevarious mechanisms for changing the temperature, pressure, and/or flowrate of the compressed working fluid 38 produced by the compressorsection 14.

The temperature of the working fluid 28 entering the compressor section14 may be changed using evaporative cooling, heat exchangers, chillers,or other temperature-altering devices known in the art. In oneparticular embodiment shown in FIG. 5, a valve 100 (such as a controlvalve, a throttle valve, a thermostatic expansion valve, or othersuitable flow control device) is operably connected to the one or morefluid conditioning devices 24 in the inlet section 12. In this instance,the fluid conditioning devices 24 are temperature-altering devices, suchas heat exchangers, chillers, or evaporative coolers. The controller 92may reposition the valve 100 to either increase or decrease heating orcooling provided to the working fluid 28 flowing through the inletsection 12. In this manner, the temperature of the working fluid 28entering the compressor section 14 may be varied, which in turn variesthe temperature, pressure, and/or flow rate of the compressed workingfluid 38 produced by the compressor section 14.

In a second embodiment shown in FIG. 5, the flow rate of the compressedworking fluid 38 produced by the compressor section 14 may be changed bychanging a flow rate of the working fluid 28 entering the compressorsection 14. As shown in FIG. 5, the system 90 includes an actuator 102or other operator operably connected to one or more inlet guide vanes104 installed in the compressor 30. The controller 92 may reposition theactuator 102 to either open or close the inlet guide vanes 104, therebyincreasing or decreasing (respectively) the flow rate of the workingfluid 28 entering the compressor section 14.

In alternate embodiments, one or more sets of stationary vanes 36 havingvariable positions, also known as variable stator vanes (not shown), maybe used to vary the flow rate of the working fluid 28 through thecompressor 30. In this configuration, the flow rate of the working fluid28 through the compressor 30 may be varied or altered, whichconsequently changes the temperature, pressure, and/or flow rate of thecompressed working fluid 38 produced by the compressor section 14.

FIG. 5 provides a third example of a suitable structure for changing thetemperature, pressure, and/or flow rate of the compressed working fluid38 produced by the compressor section 14. In this example, the system 90includes a conduit 106 (or pipe or other fluid connection) positionedbetween a downstream portion of the compressor 30 and the inlet of thecompressor 30. The controller 92 may reposition a valve 108 (such as acontrol valve, a throttle valve, a thermostatic expansion valve, orother suitable flow control device) to either increase or decrease theflow rate of the compressed working fluid 38 diverted through theconduit 106 to recirculate through the compressor section 14. Inalternate embodiments, the system 90 may include an additional heatexchanger (not shown) operably connected to the conduit 106 to eitherheat or cool the compressed working fluid 38 recirculated through thecompressor section 14. In this manner, the flow rate and/or temperatureof the compressed working fluid 38 recirculated through the compressorsection 14 may be varied, which therefore varies the temperature,pressure, and/or flow rate of the compressed working fluid 38 producedby the compressor section 14.

Another way to change the frequency, phase, amplitude, and/or coherenceof each combustor 42 is to change the fuel flow and/or fuel temperatureto one or more of the fuel circuits 82, 84, 86 in one or more combustors42. FIG. 6 provides a diagram of such a system 110 for changing thecombustion instability frequency and/or amplitude of one or morecombustors 42 by changing the fuel flow and/or fuel temperature in oneor more fuel circuits 82, 84, 86 in one or more combustors 42, accordingto alternate embodiments of the present disclosure.

Specifically, a change in the fuel pressure ratio (i.e., combustorpressure-to-fuel pressure) and/or equivalence ratio resulting fromdifferences in the fuel flow rate and/or fuel temperature may directlyaffect the combustion instability frequency and/or amplitude in eachcombustor 42. As the frequency of the combustion dynamics in one ormore, but not all, combustors 42 is driven away from that of the othercombustors 42, modal coupling of the combustion dynamics and, therefore,the coherence of the combustors 42 is reduced, which thereby reduces theability of the combustor tone to cause a vibratory response indownstream components. In addition, shifting the combustion dynamicsfrequency of each of the combustors 42 away from the natural frequencyof the downstream components may also reduce unwanted vibrations ofdownstream components.

As shown in FIG. 6, the system 110 may be incorporated into the gasturbine 10 previously described with respect to FIG. 1 and may includevarious mechanisms for changing the combustion instability frequency inone or more combustors 42 by changing the fuel flow to one or more ofthe fuel circuits 82, 84, 86 in one or more combustors 42. Although onlythree combustors 42 are shown in FIG. 6, the present invention is notlimited to any specific number of combustors 42, unless specificallyrecited in the claims.

In one particular embodiment shown in FIG. 6, the fuel flow to one ormore of the combustors 42 may be changed using a valve 112 (such as acontrol valve, a throttle valve, or other suitable flow control device)operably connected to one or more of the fuel circuits 82, 84, 86 thatsupply fuel to the combustors 42. The controller 92 may reposition eachvalve 112 in the respective fuel circuits 82, 84, 86 to increase ordecrease the fuel flow into one or more of the fuel circuits 82, 84, 86.

In other particular embodiments, the fuel flow from the one or more fuelcircuits 82, 84, 86 to one or more individual combustors 42 may bechanged. In this embodiment, individual valves 114 (such as controlvalves, throttle valves, or other suitable flow control devices) areoperably connected in one or more of the fuel circuits 82, 84, 86upstream from individual combustors 42. The controller 92 may repositioneach individual control valve 114 to change the fuel flow through one ormore fuel circuits 82, 84, 86 to one or more combustors 42, thuschanging the fuel flow to the fuel injectors 66, 68 in one or moreindividual combustors 42.

One of ordinary skill in the art will readily appreciate from theteachings herein that the individual valves 114 in one or more fuelcircuits 82, 84, 86 may be present in addition to, or instead of, thevalves 112 in the respective fuel circuits 82, 84, 86 previouslydescribed. According to this aspect of the present disclosure, the fuelflow from one or more fuel circuits 82, 84, 86 may be varied to one ormore fuel injectors 66, 68 and/or combustors 42 to change the frequency,phase, amplitude, and/or coherence of one or more combustors 42.

In yet another particular embodiment shown in FIG. 6, the combustioninstability frequency in one or more combustors 42 may be changed bychanging the fuel temperature to one or more of the fuel circuits 82,84, 86 in one or more combustors 42. As shown in FIG. 6, the system 110may include a valve 116 (such as a control valve, a throttle valve, athermostatic expansion valve, or other suitable flow control device)operably connected to one or more heat exchangers 118, which are used toadjust the temperature of the fuel to one or more of the fuel circuits82, 84, 86.

Alternately, or in addition, a separate control valve 120 and a heatexchanger 122 may be connected in one or more of the fuel circuits 82,84, 86 upstream from individual combustors 42 to similarly change thefuel temperature through one or more fuel circuits 82, 84, 86 to one ormore combustors 42. In this manner, the temperature of the fuel beingdirected to the fuel injectors 66, 68 in individual combustors 42 may bechanged. Thus, the fuel temperature through one or more fuel circuits82, 84, 86 and/or to one or more fuel injectors 66, 68 and/or combustors42 may be varied to change the frequency, phase, amplitude, and/orcoherence of the combustion instabilities of one or more combustors 42.

One of ordinary skill in the art will readily appreciate from theteachings herein that the systems 90, 110 described and illustrated withrespect to FIGS. 5 and 6 may provide various methods for the gas turbine10 to detect the possibility of unwanted vibrations in hot gas pathcomponents downstream from the combustion system and/or reduce suchunwanted vibrations. FIG. 7 provides an exemplary flow diagram ofsuitable methods of operating a gas turbine, according to variousembodiments of the present invention.

In FIG. 7, at block 124, the method may determine at least one of thefrequency, phase, amplitude, or coherence of the one or more combustioninstabilities. According to a first aspect of the present disclosure,the method may determine both the frequency and the coherence of one ormore combustion instabilities. In another aspect of the presentdisclosure, the method may determine the frequency, coherence, andamplitude of one or more combustion instabilities. In yet another aspectof the present disclosure, the method may determine the frequency,coherence, and phase of one or more combustion instabilities. In a stillfurther aspect of the present disclosure, the method may determine thefrequency, coherence, amplitude, and phase of one or more combustioninstabilities.

At block 126, the method may compare the frequency, the coherence, and,optionally, the phase and/or the amplitude, of the one or morecombustion instabilities to one or more predetermined limits todetermine if there is a likelihood of unwanted vibrations in downstreamcomponents. Such unwanted vibrations may result from coherent, in-phasecombustion instabilities. In particular embodiments, the method maydetermine two, three, or all four of the frequency, phase, amplitude,and coherence of the one or more combustion instabilities and compareeach to a separate predetermined limit to determine if there is alikelihood of unwanted vibrations in downstream components resultingfrom coherent, in-phase combustion instabilities.

If one or more of the measured characteristics are actionable relativeto their respective predetermined limits, the method may adjust at leastone parameter of the gas turbine 10 (as previously described withrespect to FIGS. 5 and/or 6) to reduce unwanted vibrations in hot gaspath components downstream from the combustion system, as indicated byblock 128. For the sake of simplicity, FIG. 7 refers to the comparisonas identifying characteristics that are “within limit(s)” or that are“limit(s) exceeded,” the latter of which is equivalent to being“actionable.” As described above, parameters that may be adjustedinclude: the temperature of the compressed working fluid produced by thecompressor section; the flow rate of the working fluid entering thecompressor section; the flow rate of the compressed working fluidrecirculated through the compressor section; the flow rate of the fueldirected to at least one fuel injector; and the fuel temperature of thefuel directed to at least one fuel injector.

One of ordinary skill in the art will readily appreciate from theteachings herein that other parameters of the gas turbine 10 may beadjusted to reduce unwanted vibrations in hot gas path componentsdownstream from the combustion system, and the present disclosure is notlimited to adjusting any particular parameter, unless specificallyrecited in the claims. If one or more of the determined characteristicsis not actionable relative to the predetermined limits, the methodreturns to block 124, and the process repeats.

According to one aspect of the present disclosure, at least oneparameter of the gas turbine is adjusted when both the frequency andcoherence of the combustion instability are actionable relative to theirrespective limits. In another aspect of the present disclosure, at leastone parameter of the gas turbine is adjusted when the frequency, thecoherence, and the amplitude of the combustion instability areactionable relative to their respective limits. In still another aspectof the present disclosure, at least one parameter of the gas turbine isadjusted when the frequency, the coherence, and the phase of thecombustion instability are actionable relative to their respectivelimits. In yet another aspect of the present disclosure, at least oneparameter of the gas turbine is adjusted when each of the frequency, thecoherence, the amplitude, and the phase are actionable relative to theirrespective limits.

In particular embodiments, the comparisons performed in block 126 mayalso incorporate a predetermined time limit into the comparison toincrease reliability and to reduce false indications of coherentconditions. For example, the comparisons performed in block 126 may alsorequire that the frequency, phase, amplitude, and/or coherence areactionable relative to their respective predetermined limits for apredetermined time interval before triggering any adjustment of the gasturbine 10 to reduce unwanted combustion-driven vibrations in downstreamcomponents.

The various embodiments described and illustrated with respect to FIGS.1-7 may provide one or more of the following advantages over existingsystems and methods for operating gas turbines 10. Specifically,changing the temperature, pressure, and/or flow rate of the compressedworking fluid 38 and/or the flow rate or temperature of the fueldirected to the combustors 42, alone or in various combinations, maydecouple the combustion dynamics and/or reduce coherence of thecombustors 42, thereby reducing unwanted vibrations in hot gas pathcomponents downstream from the combustion system. As a result, thevarious embodiments described herein may enhance thermodynamicefficiency, promote flame stability, and/or reduce undesirable emissionsover a wide range of operating levels, without detrimentally impactingthe life of the downstream hot gas path components.

This written description uses examples to disclose the invention,including the best mode, and to enable any person skilled in the art topractice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A system for operating a gas turbine, the systemcomprising: a. a compressor section configured to receive a workingfluid and to produce a compressed working fluid; b. a plurality ofcombustors downstream from the compressor section, each combustorcomprising a fuel injector, the fuel injector receiving fuel at a fueltemperature and a fuel flow rate; and c. a controller configured toexecute logic stored in a memory, the logic causing the controller: i.to determine a phase of a combustion instability and an amplitude of thecombustion instability; ii. to compare the phase of the combustioninstability to a predetermined phase limit and the amplitude of thecombustion instability to a predetermined amplitude limit; and iii. toadjust at least one parameter of the gas turbine if the phase of thecombustion instability is actionable relative to the predetermined phaselimit and the amplitude of the combustion instability is actionablerelative to the predetermined amplitude limit.
 2. The system of claim 1,wherein the compressor section further comprises a conduit forrecirculating compressed working fluid from a downstream portion of thecompressor section to an upstream portion of the compressor section; andwherein the at least one parameter adjusted by the controller is one ofa temperature of the compressed working fluid produced by the compressorsection of the gas turbine; a flow rate of the working fluid enteringthe compressor section of the gas turbine; a flow rate of the compressedworking fluid recirculated through the compressor section of the gasturbine; the fuel flow rate of the fuel to at least one injector; andthe fuel temperature of the fuel to at least one injector.
 3. The systemof claim 1, wherein the controller is further configured to compare atleast one of the phase and the amplitude of the combustion instabilityto a predetermined time limit.
 4. The system of claim 1, wherein thecontroller is further configured to determine a frequency of thecombustion instability; to compare the frequency of the combustioninstability to a predetermined frequency limit; and to adjust at leastone parameter of the gas turbine if the frequency of the combustioninstability is actionable relative to the predetermined frequency limit.5. The system of claim 1, wherein the controller is further configuredto determine a coherence of the combustion instability; to compare thephase of the combustion instability to a predetermined coherence limit;and to adjust at least one parameter of the gas turbine if the coherenceof the combustion instability is actionable relative to thepredetermined coherence limit.
 6. A system for operating a gas turbine,the system comprising: a. a compressor section configured to receive aworking fluid and to produce a compressed working fluid; b. a pluralityof combustors downstream from the compressor section, each combustorcomprising a fuel injector, the fuel injector receiving fuel at a fueltemperature and a fuel flow rate; and c. a controller configured toexecute logic stored in a memory, the logic causing the controller: i.to determine a phase of a combustion instability and a frequency of thecombustion instability; ii. to compare the phase of the combustioninstability to a predetermined phase limit and the frequency of thecombustion instability to a predetermined frequency limit; and iii. toadjust at least one parameter of the gas turbine if the phase of thecombustion instability is actionable relative to the predetermined phaselimit and the frequency of the combustion instability is actionablerelative to the predetermined frequency limit.
 7. The system of claim 6,wherein the compressor section further comprises a conduit forrecirculating compressed working fluid from a downstream portion of thecompressor section to an upstream portion of the compressor section; andwherein the at least one parameter adjusted by the controller is one ofa temperature of the compressed working fluid produced by the compressorsection of the gas turbine; a flow rate of the working fluid enteringthe compressor section of the gas turbine; a flow rate of the compressedworking fluid recirculated through the compressor section of the gasturbine; the fuel flow rate of the fuel to at least one injector; andthe fuel temperature of the fuel to at least one injector.
 8. The systemof claim 6, wherein the controller is further configured to compare atleast one of the phase and the frequency of the combustion instabilityto a predetermined time limit.
 9. A system for operating a gas turbine,the system comprising: a. a compressor section configured to receive aworking fluid and to produce a compressed working fluid; b. a pluralityof combustors downstream from the compressor section, each combustorcomprising a fuel injector, the fuel injector receiving fuel at a fueltemperature and a fuel flow rate; and c. a controller configured toexecute logic stored in a memory, the logic causing the controller: i.to determine a phase of a combustion instability and a coherence of thecombustion instability; ii. to compare the phase of the combustioninstability to a predetermined phase limit and the coherence of thecombustion instability to a predetermined coherence limit; and iii. toadjust at least one parameter of the gas turbine if the phase of thecombustion instability is actionable relative to the predetermined phaselimit and the coherence of the combustion instability is actionablerelative to the predetermined coherence limit.
 10. The system of claim9, wherein the compressor section further comprises a conduit forrecirculating compressed working fluid from a downstream portion of thecompressor section to an upstream portion of the compressor section; andwherein the at least one parameter adjusted by the controller is one ofa temperature of the compressed working fluid produced by the compressorsection of the gas turbine; a flow rate of the working fluid enteringthe compressor section of the gas turbine; a flow rate of the compressedworking fluid recirculated through the compressor section of the gasturbine; the fuel flow rate of the fuel to at least one injector; andthe fuel temperature of the fuel to at least one injector.
 11. Thesystem of claim 9, wherein the controller is further configured tocompare at least one of the phase and the coherence of the combustioninstability to a predetermined time limit.